Pushing anaerobic digestion further

On 1 December 2010, Defra published its ‘Developing an Anaerobic Digestion (AD) Framework Document’, which sets out an action plan to increase uptake of the technology in England.

Outlining the issues that need to be analysed and understood to increase energy from waste (EfW) through AD, its aim is for Government to work with industry to answer the questions posed in the draft document and develop an agreed Framework by May.

With knowledge, skills and experience gained through AD development in both continental Europe and the water sector, we commend Government on its approach to proactive engagement with industry, which has proven successful in continental Europe (e.g. Germany and Denmark).

Indeed, the learnings don’t stop there; in the European waste sector the objective of AD has traditionally been to recycle organic matter into a stable compost (digestate), with any resulting biogas treated as an added bonus. Rather than ‘copy and pasting’ from the North West European models and using AD as a solution to waste management, the Framework provides a huge opportunity for this country to position AD as a renewable energy solution (that uses waste as a feedstock). It should therefore provide incentives to build on “lessons learned” and support mechanisms for new, innovative technologies geared towards output and performance, e.g. increase MWh of renewable heat and electricity produced, enable biogas injection into the natural gas grid, improve overall fuel efficiency achieved (biogas yield and biogas conversion efficiency), improve the quality of the compost by minimising the degree of plastics present in the digestate etc.

Another vital consideration, which is referenced in the draft document, is the huge potential for co-digestion of organic waste (food waste, agricultural waste, animal by-products) and sewage sludge.

The water industry has a well established infrastructure of AD plants and extensive experience of the technology, but sewage sludge and waste are currently covered by different regulatory regimes. While discussions between the water industry, OFWAT, the Environment Agency and various trade bodies are ongoing to identify regulatory requirements and actions to facilitate compliance, without a resolution on co-digestion, it will be very difficult to develop an accurate economic model for delivering the increase in AD proposed.

This presents a great challenge and opportunity for Government, since co-digestion of sewage sludge and organic waste increases the overall efficiency of AD plants, resulting in higher biogas yields with minimal investment in new assets. Utilizing these existing sludge treatment assets as far as possible would also help to alleviate concerns over the sustainability of feedstocks and avoid “food for fuel” issues. As the draft document rightly highlights, a huge increase in AD capacity could leave these plants competing for diminishing resources (as a result of food waste reduction campaigns) or paying for purpose-grown feedstocks. Furthermore, recent EU legislation provides options to export waste to continental Europe – where countries such as The Netherlands and Germany have excess capacity in their EfW facilities – as a “secondary” fuel, adding an international dimension to the competition for waste streams.

There is no doubt that the expertise of industry, and the learning from other countries and sectors, will be vital in capitalising on the opportunities presented both by AD technology and the Government’s commitment to it. The draft Framework document is a welcome step in the right direction and provides a good basis to aid discussion. Achieving commercialisation of AD technology and facilitating access to finance is no mean feat, but there’s no need to learn this the hard way. Using all existing experience to the benefit of our emerging AD industry will be vital to the success of the final AD Framework.

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